Add support for PRODUCT_RELEASE_CONFIG_MAPS

This allows product config to determine what build flags are present in
a product's build, as well as their value.

As product config moves to a declarative specification, this can be
handled with less unnecessary work.

Bug: b/302593603
Test: manual
Change-Id: If6ae19e3da8471eaba8d6e048769f8ac6b244155